Accumulated Other Comprehensive Income (Reclassifications out of Accumulated Other Comprehensive Income) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 27, 2014	Sep. 28, 2013	Sep. 27, 2014	Sep. 28, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment income	$ 357	$ 1,129	$ 1,766	$ 3,931
Provision for income taxes	(6,594)	(7,281)	(22,180)	(34,308)
Net income	13,707	11,692	41,271	56,000
Accumulated Net Unrealized Investment Gain (Loss) [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment income	0	364	47	1,734
Provision for income taxes	0	(162)	(21)	(771)
Net income	$ 0	$ 202	$ 26	$ 963